Semiconductor processes such as epitaxy are used extensively in semiconductor processing to form very thin material layers on semiconductor substrates. These layers frequently define some of the smallest features of a semiconductor device, and they may have a high quality crystal structure if the electrical properties of crystalline materials are desired. A deposition precursor is normally provided to a process chamber in which a substrate is disposed; the substrate is heated to a temperature that favors growth of a material layer having desired properties.
It is generally desirable that the film have very uniform thickness, composition, and structure. However, due to variations in local substrate temperature, gas flows, and precursor concentrations, it is quite challenging to form films having uniform and repeatable properties. The process chamber is normally a vessel capable of maintaining vacuum, typically below 10 Torr, and heat is normally provided by heat lamps positioned outside the vessel to avoid introducing contaminants. Control of substrate temperature, and therefore of local layer formation conditions, is complicated by thermal absorptions and emissions of chamber components and exposure of sensors and chamber surfaces to film forming conditions inside the process chamber. There remains a need for a film-forming chamber with improved temperature control, and methods of operating such a chamber to improve uniformity and repeatability.